Spring中@Qualifier注解

本文对Spring中常用的IoC注解中@Qualifier注解进行补充。
当一个对象有多个实现类时，可以用@Qualifier注解来选择使用。
示例（在Spring中@PropertySource注解基础上）：
JdbcConfig类：

package config;

import com.mchange.v2.c3p0.ComboPooledDataSource;
import org.apache.commons.dbutils.QueryRunner;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Scope;

import javax.sql.DataSource;

//和spring连接数据库相关的配置类
@Configuration

public class JdbcConfig {

    @Value("${jdbc.driver}")
    private String driver;

    @Value("${jdbc.url}")
    private String url;

    @Value("${jdbc.username}")
    private String username;

    @Value("${jdbc.password}")
    private String password;

    //用于创建一个QueryRunner对象
    @Bean(name = "runner")
    @Scope(value = "prototype")
    public QueryRunner createQueryRunner(@Qualifier(value = "dataSource1") DataSource dataSource) {
        return new QueryRunner(dataSource);
    }

    //创建数据源对象
    @Bean(name = "dataSource")
    public DataSource createDataSource() {
        try {
            ComboPooledDataSource ds = new ComboPooledDataSource();
            ds.setDriverClass(driver);
            ds.setJdbcUrl(url);
            ds.setUser(username);
            ds.setPassword(password);
            return ds;
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    //创建数据源对象
    @Bean(name = "dataSource1")
    public DataSource createDataSource1() {
        try {
            ComboPooledDataSource ds = new ComboPooledDataSource();
            ds.setDriverClass(driver);
            ds.setJdbcUrl("jdbc:mysql://localhost:3306/springtest02?serverTimezone=UTC");
            ds.setUser(username);
            ds.setPassword(password);
            return ds;
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
}